The present invention relates in general to a cascaded multi-stage whirling bed drier for use in a coking plant in which at least one coking oven is periodically charged with a preheated or preliminarily dried coal, and the produced coke is subjected to a dry cooling process, whereby the equipment for the dry cooling of the coke and for the preliminary heating of the coal are interconnected by means of a common gas recirculating circuit which transfers heat released from the hot coke during the cooling to the coal to be preheated.
A method of the aforedescribed type in which the devices for dry cooling of the coke and for preheating the coal are interconnected by a common gas circulating device is described for example in the U.S. Pat. No. 3,728,230. In this known method, hot gas emerging from the dry cooling for the coke after its cooling and dust removal, is introduced as a whole into the lower part of the coal preheater in such a manner that wet coal charged into the preheater from above is brought into the condition of a whirling bed. Gas exhausted from the upper part of the coal preheater is subsequently reintroduced into the lower part of the coke dry cooler. In this mode of operation, in which coal to be preheated is brought into intermediate contact with the gas from the coke dry cooler, considerable difficulties arise in practice already from the fact that the circulating gas stream, together with the entire contents of steam which the gas has entrained in the coal preheater, is fed back into the dry cooler for the coke. Due to the high contents of steam entrained in the recirculating gas, a considerable mass of water gas is generated on the red-hot coke. Consequently, this water gas reaction brings about not only an increased fire loss of the glowing coke but also the generated explosive water gas causes naturally considerable safety problems during operation.